In the automation field, and more specifically during operational machine planning for a plant, an engineer traditionally creates a model that describes all of the machines that will be involved in the plant operation phase. This model contains a detailed description of each step that must be performed by each machine in the operational phase, as well as how these steps interact. FIG. 1 is a prior art illustration of one such planning program, where a mechanical machine operation model is shown in step 120 and contains a detailed description of each step that each machine 115 performs in the operational process, as well as how those steps interact. The model is traditionally created in the form of a sequence diagram that shows machine behavior over time in a graphical format. Today, software tools provide meta-models for describing mechanical machine operation models and allow for convenient graphical creation and editing of these mechanical models.
In order to program digital controllers to operate machines 115, mechanical machine operation model 120 is traditionally given to an engineer that is familiar with programmable logic controller (PLC) programming and he or she abstracts the mechanical model (represented at step 125) and creates at step 127 a PLC program 128 that realizes the requirements described in mechanical model 120. For example, the logic may include logic for starting/stopping signals for machines 115 in the correct timing sequence, as well as safety-critical features such as interlocks and timeout detection. The engineer typically adds sensors and actuators to the mechanical information, as those components are often missing in the original mechanical model as provided to the engineer.
The abstraction of the mechanical model developed at step 120 depends on the programming method the engineer chooses. Examples of methods for programming a PLC include STL (an assembler-like language for Siemens PLCs), Ladder Logic, and Step Chain Programming, with Step Chain Programming considered the most advanced of the three methods. If a user chooses STL, he is required to do the most abstraction, since a program must be formulated from only basic instructions. For ladder logic, the user is assisted by a ladder diagram visual display of the logic. For step chain programming, the user must identify the steps in the program based on the mechanical description (i.e., the sequence diagram) and determine the exact sequence of steps in the PLC, as well as identify the need for input signal conditions.
In each case, these traditional systems may be error-prone, due to the required manual abstraction and the complexities faced by the engineer, and may be time-consuming for the same reasons.
A system that addresses these concerns is described and disclosed in our co-pending application Ser. No. 12/547,015, entitled “Visualization Method for Electrical Machine Operation Models Based on Mechanical Machine Operation Models” for O. Noetzelmann et al., filed Aug. 25, 2009, assigned to the present assignee and herein incorporated by reference. In the Noetzelmann et al. application, a computer and display combination is used to create a combined mechanical and electrical sequence graph consisting of steps, transitions and conditions arranged by the dimensions of the participating resources as a function of time. The visualization of the model takes the form of a “display space” that is divided into device subspaces, each subspace corresponding to a different device represented by the electrical machine operation model. The ability to visualize the model provides a significant advance in the state of the art.
However, due to the restraint of a linear timeline, a sequence graph produced using this visualization process can become confusing or unclear in certain scenarios. For example, if a particular graph consists of a number of very short (in terms of “time”) steps and very long steps, the transitions between the short steps will be so compressed as to become overlapped. It then becomes difficult for the user to properly identify all of the relationships between devices and signals.
Thus, a need remains for a way to improve the performance of the above-described visualization method.